A method for operating a drive unit which includes an internal combustion engine and an automatic transmission is disclosed in U.S. patent application Ser. No. 08/050,085, filed Apr. 28, 1993, now abandoned. The drive unit is especially for motor vehicles. A drive torque is made available at the output of the transmission in dependence upon several parameters and is based on an engine torque and an engaged gear of the transmission. The driver actuates the accelerator pedal and thereby presets a desired value for the output torque independently of the gear engaged. The adjustment of the transmission ratio is achieved in that the engine is driven in its operating range wherein consumption is optimal. The engine torque is then adjusted independently of the gear which has been engaged so that the desired value for the output torque at the transmission is maintained insofar as the maximum available engine torque is adequate. The desired value is determined from the position of the accelerator pedal and, if required, from additional parameters. It is additionally provided that the transmission is driven at a high ratio while utilizing the maximum engine torque. For this reason, the engine is in its range wherein consumption is optimal. Only when the engine torque, which is required for the highest ratio, is above the maximum torque of the engine, then, generally, a lower ratio is adjusted via a threshold comparison.
A desired value for the engine torque is computed in a simple manner while considering the converter amplification in U.S. Pat. No. 5,325,740 which proceeds from the subject matter of the above-mentioned U.S. patent application Ser. No. 08/050,085. In this way, at the time point of the computation of the required engine torque, the converter amplification can already be considered which adjusts at the computed engine torque. The power determining parameters of the engine can thereby be adapted to the future requirements in correspondence to the driver command. This makes it possible to precisely provide the output desired torque in correspondence with the driver command.
Furthermore, U.S. patent application Ser. No. 08/069,060, filed Jun. 1, 1993, still pending, discloses considering lost torque of the drive unit in the above-mentioned method.
With the state of the art mentioned above, it is intended that the shift points of the transmission can be placed in consumption-optimal ranges with the aid of the so-called master shift function without it being necessary to suffer loss with respect to sportability and the capability of metering of tractive force. The consumption-optimal ranges correspond mostly to the full load boundary of the engine with the air/fuel ratio lambda=1 being maintained for exhaust-gas emission reasons. That means, however, that the shift points must be so placed that, in advance of each downshift, the engine should first be brought to its maximum engine torque in order to save fuel.